In a vehicle, conventionally, controlling of supplying electric power from a power supply to a load has been achieved by turning on and off a semiconductor switching device. In some methods of such controlling, it is employed, as the semiconductor switching device, an intelligent power device (IPD) with a passing current detecting function, a self-protective function against an overcurrent, and the like.
When using such an IPD as the semiconductor switching device, for example, it becomes possible to construct a power supply control device so that a temperature of an electrical wire connecting a power supply with a load is estimated from a passing current detected by the passing current detecting function of the IPD, and further, when the so-estimated temperature exceeds a predetermined maximum temperature, supplying electric power to the load is shut down by turning off the semiconductor switching device in view of protecting the electrical wire (see JP 2009430944 A). Additionally, for example, in a situation where it is impossible to provide for a current sufficient for driving a load by the current-carrying ability of a single IPD, it has been proposed to interpose a plurality of IPDs having the same specification, which are connected in parallel, between a power supply and the load. In this proposal, it is carried out to make the magnitude of currents passing through respective IPDs identical to each other by matching all wiring resistances of respective wiring patterns via the IPDs, thereby preventing a current from flowing in a specific IPD concentratively (see JP 2001-310720 A).